The field of art to which this invention pertains is cyanoacrylate adhesives.
Alkyl 2-cyanoacrylates, or alpha-cyanoacrylic acid esters, polymerize at room temperature in the absence of added catalysts when pressed into a thin film between two adherends. The highly polar character of the formed polymers permits the formation of very strong bonds between a wide variety of materials.
In adhesive applications, alkyl 2-cyanoacrylates are polymerized by anionic mechanism. This anionic polymerization of alkyl 2-cyanoacrylates can be initiated even at low temperatures by very weak bases, such as water and alcohol. The bonding action observed when a cyanacrylate adhesive is placed between two adherends is the result of this anionic polymerization. The catalytic effect of minute amounts of water vapor or other weak bases is maximized by spreading the adhesive into a very thin film. The presence of basic substances accelerates the bonding action of the 2-cyanoacrylates, whereas the presence of acidic materials inhibits the polymerization and can even render the adhesive inactive. The set time (elapsed time after which two surfaces that have been pressed together can no longer be moved) for cyanacrylate adhesives varies from several seconds for glass to three minutes or longer for wood. The residual moisture in glass produces bonds having extremely rapid set times whereas the slight acidity in wood, as well as wood porosity, produces bonds having somewhat slower set times.
Various attempts have been made to shorten the setting time for 2-cyanoacrylate adhesives when used on acidic and/or porous surfaces. In U.S. Pat. No. 4,170,585, the setting time for 2-cyanoacrylate adhesives is accelerated by adding to the 2-cyanoacrylate (1) polyethylene glycols having a degree of polymerization of at least 3 and (2) non-ionic surface active agents having a poly(ethyleneoxy) moiety also having a degree of polymerization of at least three.
In U.S. Pat. No. 4,307,216, adhesive compositions made from 2-cyanoacrylate esters and monoacrylates of glycol monoethers are described.
2-Cyanoacrylate ester adhesives can be modified with diacrylic acid ethers of oxyethylene glycols as described in U.S. Pat. No. 3,692,752.
Aliphatic polyols, aliphatic polyether polyols, and derivatives thereof are used to modify 2-cyanoacrylate adhesives as described in U.S. Pat. No. 4,377,490.
Dicyanoacrylate esters of glycols and polyoxyethylene glycols are disclosed in British Pat. No. 1,048,906.
The 2-cyanoacrylate ester monomer is a low viscosity liquid which possess high flowability and can penetrate into very small gaps. However, this high flowability is a disadvantage when the adhesive is applied to vertical, inclined or porous surfaces. For such uses, the adhesive compositions have been thickened by various means. As described in Japanese Kokai No. 54-107,993, a number of compounds, such as polyols, e.g., sorbitol, polyethers, e.g., polyethylene glycol dilauryl ether, polypropylene glycol dioctyl ether, polyethylene glycol dimethacrylate, aluminum salts of aliphatic acids and silicon dioxides, e.g., silica gel, are disclosed which can be used to thicken cyanoacrylate adhesive compositions.
In U.S. Pat. No. 3,607,542, adhesive compositions which can be applied to surfaces submerged in water are made from 2-cyanoacrylate esters, fillers, e.g., calcium carbonate, barium carbonate and carbon black, and, as an optional component, fumed silica. Such pastes can be applied up to about four hours after the components are mixed together.
Thixotropic cyanoacrylate adhesives which are storage stable are made from the 2-cyanoacrylate monomer and fumed silicas which are surface treated with siloxanes or silanes as described in U.S. Pat. Nos. 4,477,607 and 4,713,405.
There is a continuing search for thixotropic cyanoacrylate adhesive compositions which are storage stable and which are rapidly curable on porous, inactive, or acidic surfaces.